Richard Holdener
June 13, 2007

Step By Step

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Mmfp_0706_01z 2007_shelby_GT500_mustang Kenne_bell_twin_screw_supercharger
The new Kenne Bell twin-screw blower upgrade in the flesh.
Mmfp_0706_02z 2007_shelby_GT500_mustang Factory_eaton_roots_style_supercharger
The factory Eaton Roots-style blower is replaced by a massive 2.8L and more efficient twin-screw supercharger from Kenne Bell.
Mmfp_0706_03z 2007_shelby_GT500_mustang Supercharger_pulleys
Unlike the factory Eaton supercharger, there are a variety of supercharger pulleys to adjust the boost (and power output) to your liking.
Mmfp_0706_04z 2007_shelby_GT500_mustang Polished_kenne_bell_twin_screw_supercharger
The highlight of the Kenne Bell kit is the polished 2.8L twin-screw supercharger. Big motors deserve big blowers, and the 2.8L certainly constitutes the label BIG. Capable of supporting over 1,000 hp, it should be more than enough for all but the craziest GT500 owners.

In last issue's Part 1 of our "Mods for GT500 Mods" series, we looked at the effects of tuning and higher boost pressure on a mostly stock 5.4L motor. As you probably know, the GT500 comes factory equipped with a supercharged Four-Valve motor displacing a massive (at least for a modern Mustang) 5.4 liters.

Unlike the previous Y2K Cobra R, the Shelby/SVT gang didn't stop at a displacement hike. Taking a cue from the '03-'04 Cobra, Ford saw fit to equip the GT500 with forced induction. Not just any blower, the larger 5.4L required a brand-new Eaton supercharger. Though the blower remained a Roots style, the displacement (and therefore power potential) of the blower has grown compared to the previous 4.6L Cobra motors. As impressed as we were with the Terminator motors, these new Cyberdyne T1000 models look to be even more potent.

While the aftermarket has not yet caught up with the new Shelby, we were able to test both tuning and boost upgrades on the GT500. Our test car, supplied by Earl's Automotive, was treated to a Metco 2.59-inch blower pulley and custom tuning (23 degrees of timing and an 11.5:1 air/fuel ratio). The combination eventually allowed us to exceed 500 rwhp.

While we hope to provide more testing on a menagerie of minor mods (air intakes, exhaust, and possibly underdrive pulleys), we promised something more substantial for this issue. Rather than chip away at the performance of this GT500, we decided to go the major demolition route and installed the new Kenne Bell supercharger.

The Kenne Bell twin-screw supercharger upgrade was so impressive, it can be likened to adding a supercharger to an otherwise normally aspirated motor. Why such impressive power gains from a blower upgrade? After all, isn't the motor already equipped with a supercharger? The answer is obviously yes, but the engineers at Ford were not looking for maximum power production; they were instead looking for the most effective and cost-efficient method of reaching 500 hp. Remember, power output is only one of the design goals for any motor, and we bet the ability to dramatically increase the power output through aftermarket tuning doesn't even make the list.

Obviously, this provides the opportunities that we have come to enjoy on the previous Cobras. While a factory supercharged or turbocharged motor is a joy to behold, the lack of concern on Ford's part for future improvements means the supercharger chosen for the job was sized with only the immediate power production in mind.

Why would Ford equip the 500hp motor with a blower capable of supporting 1,000 hp? Even more importantly, why would it equip the 500hp motor with a blower that is not only twice as powerful, but twice as expensive? Enthusiasts are already complaining about the cost of the Shelby GT500 (never mind the profit-enhancing market adjustments by the individual dealerships). Installing expensive components on the motor would only aggravate the price structure. In addition to increasing the sale price of the Shelby, installing a 1,000hp blower on the 500hp motor would also increase the warranty work, since (as we all know) enthusiasts are likely to modify their motors in search of that 1,000hp mark.